I have done the diary and been alot more successful that i was when i was tested at medical, my technique has let me down and this is what i have been focusing on.

As far as the weight loss goes i have dropped from 83.5kg to 77.2kg meaning iv made the 5kg. Slightly worried that as im on the limit if my scales aren't accurate then i might miss the grade. Does anyone have any tips for last minute weight loss to get me over the line? The 5kg iv lost has been through diet change and hard work in the gym.

Dont do much exercise tonight as your muscles might hold on to water- also make sure you go to the lav before getting weighed, take off any heavy jewellery as well haha. Hope it all goes well, sounds like you have worked hard to shift it so sure it will be fine

Take as hot a bath as you can handle with Epsom salts if you have them, sit in it for 30 -40 mins and when you get out don't dry off just get dressed straight away and put a hat and socks on.
Sit like that again for as long as you can handle (the more you sweat the more weight you'll lose)
Only take sips of water even though you'll be dying for a drink - limit yourself to around 250ml total intake till after you get off the scales.

Tell somebody what your doing and to keep an eye on you incase you pass out but this is good for around 2.5 - 5lbs

Take some isotonic drinks with you for as soon as you get off the scales.

If you make it to the medical at all. Should you make it, you will be tachycardic (fast heart rate), be hypertensive (high blood pressure) and because you are dehydrated will probably have an abnormal urine test, maybe even the shakes.
There is no easy quick weight loss apart from hard work, diet and exercise - all of which you say you have done.

No worries mate, with myself not a great deal but I am reapplying. From what I can remember from my first interview they asked a little but not alot. Might be worth mentioning that I am going submariner though so I'm not too sure if that would make a difference. You can find out loads on the navy website though and that's all I really looked at before mine

I'm for submariner aswell mate, been told the wo2 thats doin the interview is the same so it will be mostly boat based, really don't want to fill my head with useless info if he's not gonna bring it up.

I know this is too late for the OP however it may be handy for others needing to loose weight.
3 times reheated pork and rancid tuna followed by some nice warm milk (leave in the sun for 3 days) will help shift some weight. Make sure you have a bucket handy to catch all the weight loss.